Method and apparatus for increasing the operating frequency of an electronic circuit

ABSTRACT

One embodiment of the present invention provides a system that facilitates temporarily increasing the operating frequency of an electronic circuit, such as a computer system, beyond a maximum sustainable operating frequency. Upon receiving a request to operate at a higher frequency, the system determines the thermal energy level of a cooling system for the circuit. If the thermal energy level is below a threshold level for the thermal capacity of the cooling system, the system increases the operating frequency of the circuit to a frequency that is greater than the maximum sustainable operating frequency for a period of limited duration. This period of limited duration is short enough to ensure that a temperature increase, caused by increasing the operating frequency, does not raise the operating temperature of the circuit above a maximum operating temperature.

BACKGROUND

1. Field of the Invention

The present invention relates to the design of electronic circuits. Morespecifically, the present invention relates to a method and apparatusfor temporarily increasing the operating frequency of an electroniccircuit beyond a maximum sustainable operating frequency.

2. Related Art

As computer system performance continues to increase at an exponentialrate, circuitry within the computer systems must keep pace withever-faster frequencies. These faster frequencies cause the circuitry toswitch more often, which causes the circuitry to consume more power. Asthe circuitry consumes more power it produces more heat.

This heat must somehow be removed so that the temperature within thecomputer circuits does not exceed a maximum operating temperature. Tothis end, computer systems typically include a number ofheat-dissipating components, such as heat sinks, cooling fans and heatpipes to dissipate thermal energy.

Unfortunately, providing these heat-dissipating components within acomputer system can present a number of problems. First, theseheat-dissipating components can significantly increase the volume andweight of a computer system, which is especially a problem for portablecomputer systems in which volume and weight must be minimized. Second,providing these heat-dissipating components can significantly increasethe manufacturing cost of a computer system. Third, providing theseheat-dissipating components can reduce reliability of a computer system,because components such as cooling fans, can fail. Furthermore, some ofthese components such as cooling fans, consume extra power and canthereby decrease battery life in a portable computer system.

In order to reduce the power consumption, many portable computer systemsenter a power conservation mode whenever the computer system is notbusy. During this power conservation mode, the computer system operatesat a reduced frequency and voltage level to minimize the amount of powerconsumed by the computer system, and to thereby increase battery life.When the computer system becomes busy again, the frequency is increasedto a maximum sustainable frequency. For many portable computer systems,this maximum sustainable frequency is determined by the capacity of thecomputer system to dissipate heat.

Note that this maximum sustainable frequency is determined by assumingthat the computer system will operate continuously at this frequency.Most computer applications, however, do not perform computational workcontinuously. In fact, most applications tend to perform computationalwork for short, concentrated bursts between long idle periods when thecomputer system is waiting for user input. Hence, the maximumsustainable operating frequency is typically too conservative because itis based on the worst-case assumption that an application performscomputational work continuously.

What is needed is a method and an apparatus for temporarily increasingthe operating frequency of a computer system beyond the maximumsustainable operating frequency.

SUMMARY

One embodiment of the present invention provides a system thatfacilitates temporarily increasing the operating frequency of anelectronic circuit, such as a computer system, beyond a maximumsustainable operating frequency. Upon receiving a request to operate ata higher frequency, the system determines the thermal energy level of acooling system for the circuit. If the thermal energy level is below athreshold level for the thermal capacity of the cooling system, thesystem increases the operating frequency of the circuit to a frequencythat is greater than the maximum sustainable operating frequency for aperiod of limited duration. This period of limited duration is shortenough to ensure that a temperature increase, caused by increasing theoperating frequency, does not raise the operating temperature of thecircuit above a maximum operating temperature.

In one embodiment of the present invention, the request for the higheroperating frequency is received from one of: an application running onthe computer system; an operating system of the computer system; or acontroller that detects an increase in computational workload bymonitoring a current sensor within the computer system.

In one embodiment of the present invention, determining the thermalenergy level of the cooling system involves measuring a temperature of aheat sink within the cooling system.

In one embodiment of the present invention, increasing the operatingfrequency involves increasing the operating frequency for an allottedtime.

In one embodiment of the present invention, increasing the operatingfrequency involves increasing the operating frequency until a command isreceived to reduce the operating frequency.

In one embodiment of the present invention, if the thermal energy levelof the cooling system is not below the threshold value, the systemincreases the operating frequency to the maximum sustainable operatingfrequency.

In one embodiment of the present invention, increasing the operatingfrequency additionally involves increasing an operating voltage of thecircuit for the period of limited duration.

In one embodiment of the present invention, after the period of limitedduration is over, the system lowers the operating frequency of thecircuit to the maximum sustainable operating frequency.

In one embodiment of the present invention, if the circuit is not busy,the system lowers the operating frequency of the circuit to a lowerpower-conserving frequency, whereby the lower power-conserving frequencyfurther decreases the thermal energy of the cooling system and therebyprovides a longer period of boosted frequency when needed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a computer system in accordance with an embodiment ofthe present invention.

FIG. 2 illustrates the use of a current sensor in accordance with anembodiment of the present invention

FIG. 3 is a flowchart illustrating the process of controlling anoperating frequency for an electronic circuit in accordance with anembodiment of the present invention.

FIG. 4A illustrates performance of a prior art system that controlspower consumption.

FIG. 4B illustrates performance of the present invention in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present invention. Thus, the present invention is notintended to be limited to the embodiments shown, but is to be accordedthe widest scope consistent with the principles and features disclosedherein.

The data structures and code described in this detailed description aretypically stored on a computer readable storage medium, which may be anydevice or medium that can store code and/or data for use by a computersystem. This includes, but is not limited to, magnetic and opticalstorage devices such as disk drives, magnetic tape, CDs (compact discs)and DVDs (digital versatile discs or digital video discs), and computerinstruction signals embodied in a transmission medium (with or without acarrier wave upon which the signals are modulated). For example, thetransmission medium may include a communications network, such as theInternet.

Computer System

FIG. 1 illustrates a computer system 100 in accordance with anembodiment of the present invention. Computer system 100 can generallyinclude any type of computer system, including, but not limited to, acomputer system based on a microprocessor, a mainframe computer, adigital signal processor, a portable computing device, a personalorganizer, a device controller, and a computational engine within anappliance.

Computer system 100 includes a number of components, including one ormore processors located within processor complex 102. These processorsare coupled to memory 116 through memory controller 115. Processorcomplex 102 can include one or more computational engines, such as amicroprocessor. Memory controller 115 can include any type of circuitrythat coordinates accesses to memory 116. Memory 116 can include any typeof random access memory for storing code and data to be accessed byprocessors within processor complex 102.

Computer system 100 also includes a number of components related tocontrolling power consumption and temperature. These components includeheat sink 112, which dissipates heat from processor complex 102. Notethat heat sink 112 can additionally dissipate heat from otherheat-producing components within computer system 100. Heat sink 112 iscoupled to thermal sensor 114, which monitors the temperature of heatsink 112.

The output of thermal sensor 114 is read by power management unit 110.Power management unit 110 generally controls the operating frequency andsupply voltage for processor complex 102. It does so by communicatingwith a special-purpose frequency/voltage controller 108, which sets theDC voltage for a switching regulator 104 and selects the outputfrequency for a programmable clock frequency generator 106. Switchingregulator 104 adjusts the switching frequency or duty cycle delivered toan output LC filter used to regulate supply voltage.

Programmable clock frequency generator 106 can be implemented in anumber of ways. One implementation uses multiple phase-lock loops(PLLs). Another implementation uses a single PLL, which includes dividedoutputs for the different frequencies (e.g., divide-by-two).

Note that some or all of the power management unit 110,frequency/voltage controller 108, switching regulator 104 andprogrammable clock frequency generator 106 can be alternativelyimplemented within processor complex 102 through software.

When the processors are not executing computationally intensive tasks,the system operates processor complex 102 at low frequency and voltagesettings. Because the cooling system is designed to radiate powerassuming worst-case power dissipation, the excess heat removal capacityof the cooling system causes a lower operating temperature when computersystem 100 is not busy processing computationally intensive tasks. Notethat for many users and applications, the ratio between idle ornear-idle time and computationally intensive time is typically quitehigh.

To execute computationally intensive tasks, processor complex 102signals power management unit 110 to request more computational speed.Power management unit 110 then adjusts the operating frequency andsupply voltage for processor complex 102 based upon the temperature ofheat sink 112. Recall that the temperature of heat sink 112 is measuredthrough thermal sensor 114. If heat sink 112 is already hot, the systemsets the frequency to a maximum sustainable operating frequency.Otherwise, if heat sink 112 is sufficiently cool, the system configuresprocessor complex 102 to run at a frequency above the maximumsustainable operating frequency until a temperature threshold isreached. The system then reconfigures the processor to operate at themaximum sustainable frequency until processor complex 102 re-enters thepower-conserving mode.

Use of a Current Sensor

FIG. 2 illustrates the use of a current sensor 204 to determine ifprocessor complex 102 is busy in accordance with an embodiment of thepresent invention. In this embodiment, frequency/voltage controller 108receives a signal from current sensor 204, which is coupled betweenpower supply 202 and processor complex 102. When processor complex 102is performing a computationally intensive task, it draws more power frompower supply 202, which causes more current to flow through currentsensor 204. This allows frequency/voltage controller 108 to determinethat processor complex 102 is performing a computationally intensivetask and can use additional computational speed.

Process of Controlling Operating Frequency

FIG. 3 is a flowchart illustrating the process of controlling anoperating frequency for an electronic circuit in accordance with anembodiment of the present invention. The process starts when anoperating system or an application requests a higher operating frequency(step 302). Note that the system can alternatively detect a greatercomputational requirement by monitoring current sensor 204 as isdescribed above with reference to FIG. 2. The system then determines thethermal energy level of the cooling system (step 304). This isaccomplished by using thermal sensor 114 to measure the temperature ofheat sink 112. Next, the system determines if this thermal energy levelis less than a threshold level by determining if the temperature of heatsink 112 is below a threshold value (step 306).

If so, the system is configured to operate for a period of limitedduration at a boosted frequency (step 308). The application or operatingsystem then operates at the boosted frequency that is greater than amaximum sustainable frequency (and possibly operates at a highervoltage) for a period of limited duration (step 310). Instead ofperforming steps 308 and 310, the system can alternatively operate atthe higher frequency until a cease command is received (step 312).

After the system is done operating at the boosted frequency (or if thethermal energy level of the cooling system is not below the thresholdlevel at step 306), the application or operating system is run at themaximum sustainable operating frequency (step 307).

Note that when the system becomes less busy, the operating frequency andvoltage can be reduced again to power-saving levels, whereby the lowerfrequency and voltage further decrease the thermal energy of the coolingsystem and thereby provide a longer period of boosted frequency whenneeded.

System Performance

FIG. 4A illustrates performance of a prior art system that controlspower consumption. In this prior art system, the power switches from alow level, P_(low), to a maximum sustainable level, P_(max), when acomputationally intensive task is being processed. Note that powerconsumption of the system is a function of the operating frequency andsupply voltage. When the operating frequency and/or the supply voltageincreases, power consumption increases. When power consumption increasesto P_(max), the temperature of the system gradually reaches a maximumtemperature, T_(max), after time, t₁.

FIG. 4B illustrates performance of one embodiment of the presentinvention. In this embodiment, the power switches from the low level,P_(low), to a boosted level, P_(boost), that is higher than a maximumsustainable power level. The temperature of the system rapidly reachesthe maximum temperature, T_(max); in time, t₂, which is shorter thantime t₁. At this point, the power consumption drops to the maximumsustainable level, P_(max).

In an exemplary configuration, one embodiment of the present inventionextracts 11% extra performance from a gigahertz microprocessor, and thetime duration for boosted operation is 42 seconds for a heat capacity of407 JIC.

Note that the relationship between temperature and frequency can beexpressed as: $\begin{matrix}{{F_{cool} = {F_{hot}\left( \frac{T_{hot}}{T_{cool}} \right)}^{n}},{{{wherein}\quad n} = {1.5.}}} & ({F1})\end{matrix}$

This formula is derived from the relationship between temperature andcharge-carrier mobility in CMOS field-effect transistors. Thesetemperatures are absolute.

Moreover, the amount of time that the processor can be operated at thisboosted frequency is given by the following equation. $\begin{matrix}{t = {{- \left( {R_{CA}C_{HS}} \right)}{\ln\left( {1 - \frac{T_{J} - {P_{b}R_{JC}} - T_{A}}{P_{b}R_{CA}}} \right)}}} & ({F2})\end{matrix}$

In this equation, T_(J) represents the junction temperature, P_(b)represents power at the boosted frequency, R_(JC) represents thermalimpedance from junction to heat sink (or case), R_(CA) representsthermal impedance from case to ambient temperature, and C_(HS)represents the thermal energy capacity of the heat sink.

The foregoing descriptions of embodiments of the present invention havebeen presented for purposes of illustration and description only. Theyare not intended to be exhaustive or to limit the present invention tothe forms disclosed. Accordingly, many modifications and variations willbe apparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the present invention. The scope ofthe present invention is defined by the appended claims.

1-33 (Canceled).
 34. A method for temporarily increasing an operatingfrequency of an electronic circuit beyond a maximum sustainableoperating frequency, comprising: monitoring the electronic circuit todetermine a need for a higher operating frequency; measuring atemperature related to the electronic circuit; and if the need for thehigher operating frequency exists, and if the temperature is below aspecified maximum, raising the operating frequency of the electroniccircuit to a value beyond the maximum sustainable operating frequency.35. The method of claim 34, wherein if the need for the higher operatingfrequency exists, and if the temperature is not below the specifiedmaximum, setting the operating frequency of the electronic circuit tothe maximum sustainable operating frequency.
 36. The method of claim 34,wherein the electronic circuit is a computer system.
 37. The method ofclaim 34, wherein measuring the temperature related to the electroniccircuit involves measuring a temperature of a heat sink that isthermally coupled to the electronic circuit.
 38. The method of claim 34,wherein increasing the operating frequency of the electronic circuitadditionally involves increasing an operating voltage of the electroniccircuit.
 39. The method of claim 34, further comprising lowering theoperating frequency of the electronic circuit to the maximum sustainablefrequency if the temperature rises above the specified maximum.
 40. Themethod of claim 34, further comprising lowering the operating frequencyto a lower power-conserving frequency when the need for the higheroperating frequency no longer exists.
 41. A computer-readable storagemedium storing instructions that when executed by a computer cause thecomputer to perform a method for temporarily increasing an operatingfrequency of an electronic circuit beyond a maximum sustainableoperating frequency, the method comprising: monitoring the electroniccircuit to determine a need for a higher operating frequency; measuringa temperature related to the electronic circuit; and if the need for thehigher operating frequency exists, and if the temperature is below aspecified maximum, raising the operating frequency of the electroniccircuit to a value beyond the maximum sustainable operating frequency.42. The computer-readable storage medium of claim 41, wherein if theneed for the higher operating frequency exists, and if the temperatureis not below the specified maximum, setting the operating frequency ofthe electronic circuit to the maximum sustainable operating frequency.43. The computer-readable storage medium of claim 41, wherein theelectronic circuit is a computer system.
 44. The computer-readablestorage medium of claim 41, wherein measuring the temperature related tothe electronic circuit involves measuring a temperature of a heat sinkthat is thermally coupled to the electronic circuit.
 45. Thecomputer-readable storage medium of claim 41, wherein increasing theoperating frequency of the electronic circuit additionally involvesincreasing an operating voltage of the electronic circuit.
 46. Thecomputer-readable storage medium of claim 41, the method furthercomprising lowering the operating frequency of the electronic circuit tothe maximum sustainable frequency if the temperature rises above thespecified maximum.
 47. The computer-readable storage medium of claim 41,the method further comprising lowering the operating frequency to alower power-conserving frequency when the need for the higher operatingfrequency no longer exists.
 48. An apparatus for temporarily increasingan operating frequency of an electronic circuit beyond a maximumsustainable operating frequency, comprising: a monitoring mechanismconfigured to monitor the electronic circuit to determine a need for ahigher operating frequency; a measuring mechanism configured to measurea temperature related to the electronic circuit; and a controllingmechanism configured to raise the operating frequency of the electroniccircuit to a value beyond the maximum sustainable operating frequency ifthe need for the higher operating frequency exists and if thetemperature is below a specified maximum.
 49. The apparatus of claim 48,wherein if the need for the higher operating frequency exists, and ifthe temperature is not below the specified maximum, setting theoperating frequency of the electronic circuit to the maximum sustainableoperating frequency.
 50. The apparatus of claim 48, wherein theelectronic circuit is a computer system.
 51. The apparatus of claim 48,wherein measuring the temperature related to the electronic circuitinvolves measuring a temperature of a heat sink that is thermallycoupled to the electronic circuit.
 52. The apparatus of claim 48,wherein increasing the operating frequency of the electronic circuitadditionally involves increasing an operating voltage of the electroniccircuit.
 53. The apparatus of claim 48, further comprising a loweringmechanism configured to lower the operating frequency of the electroniccircuit to the maximum sustainable frequency if the temperature risesabove the specified maximum.
 54. The apparatus of claim 48, furthercomprising a lowering mechanism configured to lower the operatingfrequency to a lower power-conserving frequency when the need for thehigher operating frequency no longer exists.